Various ink printing technologies have been or are being developed. One such technology, referred to as acoustic ink printing (AIP), uses focused acoustic energy to eject droplets from the free surface of a marking fluid onto a recording medium. It has been found that the principles of AIP are also suitable for the ejection of materials other than marking fluids. Those other materials include mylar catalysts, such as used in fabricating flexible cables, molten solder, hot melt waxes, color filter materials, resists, and chemical and biological compounds.
In most applications an ejected droplet must be deposited upon a receiving medium in a predetermined, possibly controlled, fashion. For example, when color printing it is very important that an ejected droplet accurately mark the recording medium in a predetermined fashion so as to produce the desired visual effect. The need for accurate positioning of ejected droplets on a receiving medium makes it desirable to droplets of the different colors in the same pass of the printhead across the recording medium, otherwise slight variations between the relative positions of the droplet ejectors and the receiving medium, or changes in either of their characteristics or the characteristics of the path between them, can cause registration problems (misaligned droplets).
The application of color printing can be used to illustrate the need for accurate droplet registration. To produce a predetermined color on a recording medium using AIP, the proper amounts of a number of different color inks have to be deposited in relatively close proximity. Without accurate registration of the droplets of the different colors the perceived color is incorrect because of overlap of some droplets (which produces an incorrect color at the overlap) and exposure (noncoverage) of the underlying receiving medium (which adds another color, that of the receiving medium, to the mix). Another application where extremely accurate control of ejected droplets is important is when forming small samples of overlapping proteins. Without proper registration, the desired protein sample is not obtained. Because of the need expressed for accurate volume depositions (reference P. Morales and M. Sperandei, "New method of deposition of biomolecules for bioelectronic purposes," Appl Phys. Lett. 64, pp. 1042-1044 (particularly pp. 1043) 21 Feb. 1994), it should be noted that since acoustically ejected droplets have very small, but accurately controlled, volumes, that acoustic droplet ejectors are particularly useful for depositing proteins.
One common attribute of both color printing and protein experimentation is that more than one material is involved. Therefore, when using acoustic ejection for color printing, protein experimentation, or other applications where more than one material is being ejected, it is beneficial to use a material deposition head with multiple ejector units. By material ejection head it is meant a structure from which droplets of one or more materials are ejected. By "ejector unit" it is meant a structure capable of ejecting a selected material from an associated chamber which is either the only chamber, or is one that is isolated from the other chambers. Therefore, a material deposition head with multiple ejector units is a structure capable of ejecting multiple materials. In terms of color printing, a material deposition head with multiple ejector units is a printhead capable of holding and ejecting more than one color of ink.
In the prior art is the technique of abutting individual ejector units together to achieve a material ejection head with multiple ejector units. However, as the required droplet placement accuracy increases, as more ejector units having more individual droplet ejectors are required, and as low cost becomes more important, the abutting of individual ejector units to form a material ejection head with multiple ejector units becomes problematic.
Therefore, a material deposition head having a plurality of ejector units, each having a plurality of accurately located individual droplet ejectors, and which are accurately located relative to each other, is desirable. Furthermore, a technique for fabricating such a material deposition head having a plurality of ejector units, each having a plurality of accurately located individual droplet ejectors, and which are accurately located relative to each other, is also desirable. Beneficially, to achieve tight droplet registration at low cost such a material deposition head would have lithographically defined ejector units.
More detailed descriptions of acoustic droplet ejection and acoustic printing in general are found in the following U.S. Patents and in their citations: U.S. Pat. No. 4,308,547 by Lovelady et al., entitled "LIQUID DROP EMITTER," issued 29 Dec. 1981; U.S. Pat. No.4,697,195 by Quate et al., entitled "NOZZLELESS LIQUID DROPLET EJECTORS," issued 29 Sep. 1987; U.S. Pat. No. 4,719,476 by Elrod et al., entitled "SPATIALLY ADDRESSING CAPILLARY WAVE DROPLET EJECTORS AND THE LIKE," issued 12 Jan. 1988; U.S. Pat. No. 4,719,480 by Elrod et al., entitled "SPATIAL STABLIZATION OF STANDING CAPILLARY SURFACE WAVES," issued 12 Jan. 1988; U.S. Pat. No. 4,748,461 by Elrod, entitled "CAPILLARY WAVE CONTROLLERS FOR NOZZLELESS DROPLET EJECTORS," issued 31 May 1988; U.S. Pat. No. 4,751,529 by Elrod et al., entitled "MICROLENSES FOR ACOUSTIC PRINTING," issued 14 Jun. 1988; U.S. Pat. No. 4,751,530 by Elrod et al., entitled "ACOUSTIC LENS ARRAYS FOR INK PRINTING," issued 14 Jun. 1988; U.S. Pat. No. 4,751,534 by Elrod et al., entitled "PLANARIZED PRINTHEADS FOR ACOUSTIC PRINTING," issued 14 Jun. 1988; U.S. Pat. No. 4,959,674 by Khri-Yakub et al., entitled "ACOUSTIC INK PRINTHEAD HAVING REFLECTION COATING FOR IMPROVED INK DROP EJECTION CONTROL," issued 25 Sep. 1990; U.S. Pat. No. 5,028,937 by Khuri-Yakub et al., entitled "PERFORATED MEMBRANES FOR LIQUID CONTRONLIN ACOUSTIC INK PRINTING," issued 2 Jul. 1991; U.S. Pat. No. 5,041,849 by Quate et al., entitled "MULTI-DISCRETE-PHASE FRESNEL ACOUSTIC LENSES AND THEIR APPLICATION TO ACOUSTIC INK PRINTING," issued 20 Aug. 1991; U.S. Pat. No. 5,087,931 by Rawson, entitled "PRESSURE-EQUALIZED INK TRANSPORT SYSTEM FOR ACOUSTIC INK PRINTERS," issued 11 Feb. 1992; U.S. Pat. No. 5,111,220 by Hadimioglu et al., entitled "FABRICATION OF INTEGRATED ACOUSTIC INK PRINTHEAD WITH LIQUID LEVEL CONTROL AND DEVICE THEREOF," issued 5 May 1992; U.S. Pat. No. 5,121,141 by Hadimioglu et al., entitled "ACOUSTIC INK PRINTHEAD WITH INTEGRATED LIQUID LEVEL CONTROL LAYER," issued 9 Jun. 1992; U.S. Pat. No. 5,122,818 by Elrod et al., entitled "ACOUSTIC INK PRINTERS HAVING REDUCED FORCUSING SENSITIVITY," issued 16 Jun. 1992; U.S. Pat. No. 5,142,307 by Elrod et al., entitled "VARIABLE ORIFICE CAPILLARY WAVE PRINTER," issued 25 Aug. 1992; and U.S. Pat. No. 5,216,451 by Rawson et al., entitled "SURFACE RIPPLE WAVE DIFFUSION IN APERTURED FREE INK SURFACE LEVEL CONTROLLERS FOR ACOUSTIC INK PRINTERS," issued 1 Jun. 1993. All of those patents are hereby incorporated by reference.